1. Field of the Invention
This invention relates to metal structures resistant to the harmful effects of concurrent oxidation and corrosion by aqueous electrolyte, and which are capable of conduction between the structure surface and an aqueous electrolyte when made anodic in said electrolyte. This invention more specifically relates to electrode structures for use in plates for lead-acid electric storage batteries and as electrodes for use in other electrochemical processes, usually in contact with an aqueous acidic electrolyte. It is a companion invention to an invention described in a concurrently filed application by the same inventors entitled Negative Electrode for Lead-Acid Storage Battery.
2. Definitions
For the purposes of clarity and conformity in the specification and the claims, the following terms will be defined.
The term "anodically passivatable metal" shall mean a metal which, when in contact with an electrolyte and made anodic within an effective potential range, becomes passive to that electrolyte, usually by formation of an oxidic film. For the purposes of the definition in this application, this oxidic film is a non-conductor of electricity.
The term "valve metal" shall mean an anodically passivatable metal, which metal when made cathodic in the electrolyte in which the metal acting as an anode becomes passivated, readily permits passage of current between the metal surface and the electrolyte, and which rapidly or intantaneously passivates when the current is reversed.
The term "matrix metal" includes the primary valve metals niobium, tantalum, titanium, zirconium and hafnium, and alloys containing more than about 85% of these valve metals and exhibiting essentially the same electrochemical valve characteristics as these metals. Matrix metal also includes silicon-containing materials which anodically form silicon dioxide rich surface coatings as well as aluminum and other anodically passivatable metals which may be severely limited with respect to electrolytes with which they can be used.
The terms "filling metal" or "infiltrating metal" shall include lead, and all metals that may be used in electric storage battery grids, such as tin and antimony, and alloys of lead and these metals as well as all other metals, (for example, manganese and ruthenium) which are characterized by having an electrochemically producible oxide which is an electroconductor and which is insoluble in a given aqueous electrolyte. A filling metal can also contain any dopants which may be added to it in order to impart certain desired characteristics. Dopants in lead may be calcium, arsenic, antimony, tin, silver, etc.
The term "oxidized filling metal" shall include oxidized products of the filling metal such as PbO.sub.2, SnO.sub.2, Sb.sub.2 O.sub.5 or mixtures thereof, along with any dopants or possible contaminate from the path walls of matrix metal, such as TiO.sub.2. When formulae such as PbO.sub.2, MnO.sub.2, etc., are used herein especially in regard to electroconductive oxides, it is to be observed that these oxides are not limited to exact stoichiometric compounds but rather include, for example, non-stoichiometric species such as PbO.sub.1.9 which are well known to have enhanced electrical conductivity compared to true stoichiometric compounds.
The term "structural electrode member" shall mean that portion or portions of an electrode which provides mechanical strength to the electrodes as well as a path for electric conduction within the electrode. When this term is used in the context of a battery, it refers to the positive grid and does not include the active material which is in electrically conductive contact with the structural member. However, in the context of other electrochemical processes, for example, electrowinning, this term refers to the whole of the electrode.
The term "composite electrode" shall mean an electrode having a structural electrode member constructed in accordance with the invention disclosed and claimed herein, wherein the structural electrode member includes a composite of a matrix metal and filling metal. The structural electrode member may comprise the entire composite electrode, or only one of several elements.
Any reference in this specification to a particular metal or alloy as the matrix metal, filling metal or coating metal is made by way of example and not for the purpose of limiting the scope of the invention.